Endgame Entertainment has come onboard as financier of “Bitter Pill,” the Steven Soderbergh pic formerly known as “Side Effects.”

Scott Z. Burns scripted the psychological thriller.

Deal, announced Tuesday, comes after Megan Ellison’s Annapurna backed off from financing the film last week. Endgame said it’s in discussions with 1984 Private Defense Contractors (“The Grey”) to co-finance.

Producers said they’re in discussions with Rooney Mara, Jude Law, Channing Tatum and Catherine Zeta Jones to star. Plot details are being kept under wraps; shooting will start in April.

Open Road Films announced on Jan. 18 that it had acquired U.S. distribution rights, with a release planned for the first half of 2013. Filmnation is handling international sales on behalf of Endgame and will introduce the film to buyers at the Berlin Film Festival.

As previously announced, Lorenzo di Bonaventura is producing the film with Gregory Jacobs and Burns. Endgame’s James D. Stern and Douglas E. Hansen will join the project as exec producers.

“Steven Soderbergh continues to be one of the most innovative and original directors making films today,” Stern said. “Endgame can’t wait to work with him on what promises to be an exciting commercial thriller.”

Endgame’s move to finance the film comes three months after it launched an ambitious marketing venture dubbed Endgame Releasing to partner with equity investors, third-party producers and studios to provide P&A funding for wide-release films. Endgame’s deal was negotiated for “Bitter Pill” was negotiated by Stern and Hansen for the company and by UTA on behalf of the filmmakers.